Efficient solution route to transparent ZnO semiconductor films using colloidal nanocrystals

•ZnO nanocrystals (NCs) assembled films were fabricated on a ITO coated glass substrate by a simple drop-casting method using the NC suspension in toluene.•The film had transmittance of more than 80% in the visible to near-infrared region, showing good optical transparency.•A device coupling the ZnO NC film with a Cu2ZnSnS4 (CZTS) NC film exhibited an obvious diode-like current–voltage behavior and a PV response when using CdS layer.